I do not agree with my school here, for I cannot think a comet is a 1 sudden fire, but I rank it among Nature’s permanent creations. First of all, everything that the atmosphere creates is short-lived; such things arise in an element that is fugitive and changeable. How can anything continue the same for long in the air, which itself never remains the same? It is always in a state of flux, and its quiet is short-lived. It changes within a brief moment to another condition from that in which it had been. It is now rainy, now clear, now alternates from one to 2 the other. The clouds, so intimately connected with it, into which it collects and from which it is released again, now gather, now disperse, but never remain at rest. Fire cannot possibly abide securely in a volatile body, nor can it keep its place so persistently as does a fire that Nature has fixed never to be dislodged. Further, if the fire stuck close to its fuel, it would always sink. For the air is the thicker, 3 the nearer it is to the earth. But a comet is never depressed to the lowest strata of the atmosphere, nor does it ever approach the ground. Besides, fire either goes in the direction its nature prompts, that is, upwards, or else in the direction in which it is drawn by the material on which it has fastened, and on which it feeds. XXIII In none of the ordinary fires in the sky is the route curved; it 1 is distinctive of a star (planet) that it describes a curve in its orbit. Whether other comets had this circular orbit I cannot say. The two in our own age at any rate had. Again, everything kindled by a temporary cause quickly gives out. Thus torches gleam only while they flit across the sky; thus lightning has strength for just one stroke; thus so-called shooting and falling stars fly past, cutting through the air. No fires have any considerable duration unless 2 their strength is inherent. I mean the divine fires which the universe maintains eternally, because they are its parts and works. These, I say, are always active; they have an orbit the even tenor of which they preserve, and they are uniform. They would on alternate days be larger or smaller if the fire was merely casual, the sudden outcome of some accidental cause. Such a fire would be greater or less according as it was fed more abundantly or more scantily. I said a moment ago that no fire could be lasting which arose from some defect in the atmosphere. I have now to add further, that it can by no means be fixed and steady. 3 Both torch and lightning and shooting star, and any other kind of fire forced out of the air by pressure, are in flight; none of them is visible save in the course of its fall. But a comet has its own settled position. For that reason it is not expelled in haste, but steadily traverses its course; it is not snuffed out, but takes its departure. If it were a wandering star (_i.e._ planet), says some one, it would be in the zodiac.